But this is a very small part of the work accomplished. The worms are in league with the farmer; are, in fact, his unappreciated assistants, upon whose endeavors depends much of the success of his crops. They are continually swallowing the earth, and depositing it at the surface, and working it over and over. If I should ask my young readers to estimate the quantity of earth brought to the surface in a single acre in a year, I fear they would not place the amount as high as Mr. Darwin, who states that the vegetable mould thus transported in some places amounts to ten tons an acre. Think of it! If your ten-acre farm is in one of these favored localities, these silent workers, say to the number of a million, have ploughed up about one hundred tons of earth for you, giving you a fine top dressing. The worms not only carry all this material to the surface, but they drag vast quantities of leaves and other matter down, that serve to enrich the soil and render it capable of producing larger crops. They cover up seeds and other objects to a remarkable extent; and a flat rock set upon the ground will soon become buried, through their means. Some of the most interesting parts of Roman villas found in England have been, according to Darwin, preserved in this way; the worms undermining them, and gradually heaping soil over the walks and slabs, until finally, aided by other causes, they disappeared beneath the ground. The earthworms of Australia attain a large size,--sometimes several feet in length,--and have been seen climbing trees. Some casts found in India are a foot in length. The worms evidently live in complete darkness; but it is known that at certain times, and under certain conditions, they are luminous: so that a state of things may exist under the ground of which we have no conception, and the tunnels of these little creatures may be brightly illumined. We have never been so fortunate as to observe their phosphorescence, but Dr. Phipson says, “I distinctly remember witnessing, when a child, the phosphorescence of the earthworm. The light appeared connected with the mucus that covered the animal’s body.” And other naturalists have observed the light under certain conditions. If they possess this property to a greater extent than we are now aware of, it must be a fatal gift, as the sharp little eyes of the mole, though not remarkable for their powers of observation, would probably catch the faintest gleam. These animals are continually upon the forage; and their appetites can be imagined from an actual experiment, which showed that two moles devoured in nine days 341 grubs, 193 earthworms, 25 caterpillars, and a mouse,--skin, bones, and all!